Cyclostratigraphy and astrochronology of the Tripoli diatomite formation (pre-evaporite Messinian, Sicily, Italy)

The ongoing debate about the Messinian salinity crisis in the Mediterranean is fuelled in part by the lack of an adequate time control. The most accurate and, at the same time, detailed constraints are nowadays provided by the astronomical dating technique. Here we present an astronomical age model for the cyclically bedded Tripoli diatomite Formation on Sicily (pre-evaporite Messinian, Italy) based on an integrated stratigraphic study of three key-sections, Falconara, Gibliscemi and Capodarso. Characteristic sedimentary cycle patterns allow (i) the sections to be cyclostratigraphically correlated, the 'bed-to-bed' correlations being confirmed by high-resolution planktonic foraminiferal biostratigraphy, and (ii) the Tripoli cycles to be calibrated to the astronomical record. Despite minor misfits the correctness of the tuning is evident from the match between precession-obliquity interference in the astronomical target and its reflection in the sedimentary cycle record. The tuning provides absolute astronomical ages for all sedimentary cycles and planktonic foraminiferal events. The base of the Tripoli is astronomically dated at 7.005 Ma, indicating that the onset of diatomite formation is diachronous in the Mediterranean since it started 300 000 years earlier on Sicily than on Gavdos, south of Crete. The top of the Tripoli, and thus the onset of the salinity crisis proper on Sicily, arrives at 5.98 Ma.